FMEA Failure Modes & Effects Analysis

FMEA Failure Modes & Effects Analysis By Sherif M. Eltoukhi Summer Trainee Quality Assurance Department August 2011

Table Of Contents Introduction.................................3

FMEA Implementation.................14

History of FMEA.........................4

The pre-work.........................15

Reasons For FMEA....................5

Actual FMEA.........................17

Advantages of FMEA..................6

Calculating the RPN..............23

Time For FMEA...........................7

Example of FMEA.......................26

Types of FMEA...........................8

limitations for FMEA....................27

Important Definitions...................9

Important Notes..........................30

Steps For FMEA........................11

FMEA Software...........................31

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Introduction A failure modes and effects analysis (FMEA) is a procedure in product development and operations management for analysis of potential failure modes within a system for classification by the severity and likelihood of the failures. A successful FMEA activity helps a team to identify potential failure modes based on past experience with similar products or processes, enabling the team to design those failures out of the system with the minimum of effort and resource expenditure, thereby reducing development time and costs. Widely used in manufacturing industries in various phases of the product life cycle and is now increasingly finding use in the service industry.

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History of FMEA Procedures for conducting FMECA were described in US Armed Forces Military in 1949. Later it was used for aerospace/rocket development to avoid errors in small sample sizes of costly rocket technology.(Ex.Apollo Space) program later the food industry in general.The primary push came during the 1960s, while developing the means to put a man on the moon and return him safely to earth. In the late 1970s the Ford Motor Company introduced FMEA to the automotive industry for safety and regulatory consideration PFMEA Now extensively used in a variety of industries including semiconductor processing, software, and healthcare. Toyota has taken this one step further with its Design Review Based on Failure Mode (DRBFM) approach. The method is now supported by the American Society for Quality (ASQ) which provides guides on applying it.

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Reasons For FMEA 1. Development of system requirements that minimize the likelihood of failures. 2. Development of methods to design and test systems to ensure that the failures have been eliminated. 3. Evaluation of the requirements of the customer to ensure that those do not give rise to potential failures. 4. Identification of certain design characteristics that contribute to failures, and minimize or eliminate those effects. 5. Tracking and managing potential risks in the design. This helps avoid the same failures in future projects. 6. Ensuring that any failure that could occur will not injure the customer or seriously impact a system. 7. To produce world class quality products. 5

Advantages of FMEA 1. Improve the quality, reliability and safety of a product/process. 2. Improve company image and competitiveness. 3. Increase customer satisfaction. 4. Reduce system development timing and cost. 5. Collect information to reduce future failures, Emphasize problem prevention. 6. Early identification and elimination of potential failure modes. 7. Minimize late changes and associated cost. 8. Catalyst for teamwork and idea exchange between functions. 9. Reduce possible scrap in production.

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Time For FMEA The FMEA should be updated whenever:

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At the beginning of a cycle (new product/process).

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Changes are made to the operating conditions.

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A change is made in the design.

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New regulations are instituted.

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Customer feedback indicates a problem.

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Types Of FMEA ■

Process: analysis of manufacturing and assembly processes.

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Design: analysis of products prior to production.

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Concept: analysis of systems or subsystems in the early design concept stages.

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Equipment: analysis of machinery and equipment design before purchase.

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Service: analysis of service industry processes before they are released to impact the customer.

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System: analysis of the global system functions.

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Software: analysis of the software functions.

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Important Definitions 1. Failure: The LOSS of an intended function of a device under stated conditions. 2. Failure mode: The manner by which a failure is observed; it generally describes the way the failure occurs. 3. Failure effect: Immediate consequences of a failure on operation, function or functionality, or status of some item. 4. Indenture levels: An identifier for item complexity. Complexity increases as levels are closer to one. 5. Local effect: The Failure effect as it applies to the item under analysis. 6. Next higher level effect: The Failure effect as it applies at the next higher indenture level.

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Important Definitions 7. End effect: The failure effect at the highest indenture level or total system. 8. Failure cause: Defects in design, process, quality, or part application, which are the underlying cause of the failure or which initiate a process which leads to failure. 9. Severity(S): The consequences of a failure mode. Severity considers the worst potential consequence of a failure, determined by the degree of injury, property damage, or system damage that could ultimately occur. 10. Occurrence(O): to look at the cause of a failure mode and the number of times it occurs. by looking at similar products or processes and the failure modes that have been documented for them. 11. Detection(D): to measures the risk that the failure will escape detection. 12. Risk Priority Number(RPN): RPN = S x O x D

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Steps For FMEA

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Steps For FMEA 1.

Select a process.

2.

Form a team .

3.

Analyze the process.

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Brainstorm about the potential failure modes & their effects.

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Find the root cause of these modes.

6.

List the current control.

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Assign the Severity(S), Occurrence(O) & Detection(D).

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Calculate the Risk Priority Number(RPN).

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Take actions to reduce the RPN.

10. Reevaluate the RPN.

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Steps For FMEA 1.

Select a process.

2.

Form a team .

3.

Analyze the process.

4.

Identify strategies for improvement.

5.

Implement strategies.

6.

Evaluate the effectiveness of taken actions.

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FMEA Implementation In FMEA, Failures are prioritized according to:

• • •

How serious their consequences are. How frequently they occur. How easily they can be detected.

A FMEA also documents current knowledge and actions about the risks of failures for use in continuous improvement. FMEA is used during the design stage with an aim to avoid future failures (sometimes called DFMEA in that case). Later it is used for process control, before and during ongoing operation of the process. Ideally, FMEA begins during the earliest conceptual stages of design and continues throughout the life of the product or service. The outcomes of an FMEA development are actions to prevent or reduce the severity or likelihood of failures, starting with the highest-priority ones. 14

FMEA Implementation The Pre-work Before starting with an FMEA, it is important to complete some pre-work to confirm that robustness and past history are included in the analysis. A robustness analysis can be obtained from interface matrices, boundary diagrams, and parameter diagrams. Many failures are due to noise factors and shared interfaces with other parts and/or systems, because engineers tend to focus on what they control directly.

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FMEA Implementation FMEA pre-work is developed in three main phases: 1- Describe the system and its function. 2- Create a block diagram of the system. This diagram gives an overview of the major components or process steps and how they are related. These are called logical relations around which the FMEA can be developed. It is useful to create a coding system to identify the different system elements. The block diagram should always be included with the FMEA. 3- Create a worksheet. which contains the important information about the system, such as the revision date or the names of the components. On this worksheet all the items or functions of the subject should be listed in a logical manner, based on the block diagram.

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FMEA Implementation The Actual FMEA Actual FMEA is developed in three main phases, in which appropriate actions need to be defined: Step 1: Occurrence In this step it is necessary to look at the cause of a failure mode and the number of times it occurs, by looking at similar products or processes and the failure modes that have been documented for them. All the potential causes for a failure mode should be identified and documented. this should be in technical terms. A failure mode is given an occurrence ranking (O) from 1:10. Occurrence also can be defined as %.

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FMEA Implementation The Actual FMEA Actual FMEA is developed in three main phases, in which appropriate actions need to be defined: Step 1: Occurrence Ranking is giving according to the following table: Ranking 1 2/3 4/5/6 7/8 9/10

Meaning No known occurrence on similar products Low (Relatively few failures) Moderate (Occasional failures) High (Repeated failures) Very High (Failures))is almost inevitable)

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FMEA Implementation The Actual FMEA Actual FMEA is developed in three main phases, in which appropriate actions need to be defined: Step 2: Severity In this step determine the ultimate effect of each failure mode. All the potential effects of a failure mode should be identified and documented. this should be in terms of what the user might see or experience. Each effect is given a severity number (S) from 1:10 Actions need to be determined if the severity is high.

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FMEA Implementation The Actual FMEA Actual FMEA is developed in three main phases, in which appropriate actions need to be defined: Step 2: Severity Number is giving according to the following table: Ranking 1 2 3 3 4/5/6 33 7/8 9/10

Meaning No effect Very minor (Only noticed by discriminating customers) )) Minor (Noticed by average customers)

)) Moderate (Most customers are annoyed) High (Cause a loss of primary function, Customers are dissatisfied) )) Very High & Hazardous (Inoperative product, Customers angered, Unsafe or possible injury) 20

FMEA Implementation The Actual FMEA Actual FMEA is developed in three main phases, in which appropriate actions need to be defined: Step 3: Detection In this step it is necessary to test the actions taken efficiency. The detection ranks the ability of planned tests and inspections to remove defects or the risk that the failure will escape detection.However, The proper inspection methods need to be chosen. An assigned detection number (D) is given from 1:10. A high detection number indicates that the chances are high that the failure will escape detection, or that the chances of detection are low.

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FMEA Implementation The Actual FMEA Actual FMEA is developed in three main phases, in which appropriate actions need to be defined: Step 3: Detection Number is giving according to the following table: Ranking 1

Meaning Almost certain

2

High

3 3 4/5/6 33 7/8

Moderate Moderate (Most customers are annoyed) Low

9/10

Very remote to absolute uncertainty 22

FMEA Implementation Calculating the RPN RPN play an important part in the choice of an action against failure modes. They are threshold values in the evaluation of these actions. After ranking the severity, occurrence and detectability the RPN can be easily calculated by multiplying these three numbers:

RPN = S × O × D This has to be done for the entire process and/or design. Once this is done it is easy to determine the areas of greatest concern. RPN could be between 1 (Absolute best) & 1000 (Absolute Worst).

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FMEA Implementation Calculating the RPN The failure modes that have the highest RPN should be given the highest priority for corrective action. This means it is not always the failure modes with the highest severity numbers that should be treated first. There could be less severe failures, but which occur more often and are less detectable.

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FMEA Implementation After these values are allocated, recommended actions with targets, responsibility and dates of implementation are noted. These actions can include

• • •

specific inspection, testing or quality procedures. Redesign (such as selection of new components). Adding more redundancy and limiting environmental stresses or operating range.

Once the actions have been implemented in the design/process, the new RPN should be checked, to confirm the improvements. These tests are often put in graphs, for easy visualization. Whenever a design or a process changes, an FMEA should be updated.

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Example of FMEA

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Limitations For FMEA 1. Since FMEA is effectively dependent on the members of the committee which examines product failures, it is limited by their experience of previous failures. If a failure mode cannot be identified, then external help is needed from consultants who are aware of the many different types of product failure. FMEA is thus part of a larger system of Quality control, where documentation is vital to implementation. 2. If used as a top-down tool, FMEA may only identify major failure modes in a system. Fault tree analysis(FTA) is better suited for "top-down" analysis. When used as a "bottom-up" tool FMEA can augment or complement FTA and identify many more causes and failure modes resulting in top-level symptoms. But it won’t be able to discover complex failure modes involving multiple failures within a subsystem.

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Limitations For FMEA 3. The multiplication (RPN) of the severity, occurrence and detection rankings may result in rank reversals, where a less serious failure mode receives a higher RPN than a more serious failure mode. The reason for this is that the rankings are ordinal scale numbers, and multiplication is not defined for ordinal numbers.

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Limitations For FMEA Thus The Critical number should be taken into consideration, Where

Critical Number = S x D

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Important Notes ■ Try to eliminate the failure mode (some failures are more preventable than others). ■ Minimize the severity of the failure. ■ Reduce the occurrence of the failure mode. ■ Improve the detection.

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FMEA Software Most FMEAs are created as a spreadsheet. Specialized FMEA software packages exist that offer some advantages over spreadsheets.

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Thanks =)

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